Interlocking system for railroads



March 3,1931. .1. c. LINDNER INTERLOCK ING SYSTEM FOR RAILROADS FiledDec. '14. 1929 mm Y L 1 E:

Patentecl Mar. 3, 1931 JOHN C. LINDNER, or nocnns'rnn, nnw yomiAssrenonmo GENERAL nAI WAY' SIGNAL COMPANY, on nocnnsmncmwnw Year: p v

InrnnLocKnve sYsTnM non mes Application filed neeem eriareeegf Serial naimes.

This invention relates to electric inter,- loclring sy-ste1ns{fOrraih-Oads, and more par ticularly pertains to cross protection meansfor such systems.

In'interlocking plants}, it is desirable to provide-means in the centraltower for continuously indlcatmg the position and locked condition ofthe outlying track switches, so that the signals, governing the trafilcovera particular track switch, may be selected orcontr'olled inaccordance'with the condition of that PRPtlCUlEI-F'SWItCh. In one typeotsystem, this has been accomplished by con; trolling athree-position-relay, located in the tower, over a polarized linecircuit extending from the associated switch. Such a switch repeatingrelay, sometimes calledan SSrelay, whencont-rolled over a "polarizedline circuit, is of course provided withall the desirable features ofcross protection inherentin such a circuit, all of which is well knownto those skilled in the art. In accordance with the present invention,

it is proposed to provide a switch machine control-system of the dynamicindication type which has the control of a switch repeating or relaysuper-imposed upon it by the use of alternating current. One object ofthe present inventionis to provide. such'superimposed SSre'laycontrol ina manner to retain the inherent'cross protection offa polarized circuitfor thef SS relay, and also tohave' this super-imposed control check thecross 7 protection: ofthe switch machine contro-l ci'rdrawing, and inpart pointed; cut es: the dec'uits. A; further object is to prcvideprotection for both the switch machine control and'the SS relay control,from crosses with the control wires of other similarly operatedfunctions and also from crosses with foreign sources.

(Ether objects, purposes and characteristic features of thefpresentinvention will be in part obvious from the accompanying scription of theinvention progresses.

In describing the invention in det'ail', reference Wlll be made to thesmglefigure of the accompanying drawing, in which an inter lockingsystem embodying the present in V ventron has been shown in "adiagrammatic manner'il lustrating the control of two typical trackswitches of an" interlocking plant 3 and} g alsothe' indication meansassogziated there With.

lar'retfierence characters having the distinctive exponentsaiandtrespectively 1 VV'th reference'to the singlefigure oi the accompanyingdrawing twomain tracks, having rails '55 and 6 respectively, are shownintercoi'inected' by' rails 7 of a crossover at each end of which arelocated'track switches TS"? and TS respectively. These tra'cks switchesTS and TS are 'normally s'et tor mainline The similar-devices associatedwith" 1 each 'trackswitch will be designated by simi- 1,466,903, datedSeptember4, 1923. I These I switch mac'hinesinclude their respectivepole changer contacts PC and'lEG and their respectivepole changercoilcontacts PUG and PGC L" Also, pointdecte'ctor contacts 1 1)? and PDare associated with these respec t-ive switch machines andtrack-switches; Y

Pole changer contacts PC include movable contacts 10 I and :11-,fvvhiljepole, changer con tacts PC include movable contactslQ and'l3.'- Thesemovable contacts: of the respective switch machines make contactbetweencertain pairs of fixed 'contacts whenfiin new r ex tremepositions and make contact: between other palrs of fixed contacts wheninfrever's'e extreme positions .lhejnormal or reverse positions of thesemovable contacts are mechani' sally caused to be ,assumed'incorrespondence with the respective switch machineat the end of anoperation; 01 are electrically caused to assume-opposite positionsduring the operationof the switch inachine,in a manner asset forth inthe above mentioned Patent "No. Ihe pole changer coil contacts 'PCC -andPCC include movable contacts '14 and 'l5 re spectively whichmake contactbetween theirf;

respective pairs-of fixedcontactswheninnoi f l mal extreme positions erin intermediate "positions; and also movable contacts 16 and 17respectively which make contact betwen their respective pairs of fixedcontacts when in reverse extreme positions or in intermediate positions.

The point detector contacts PD include movable contacts 18 and 19 whichassume normal or reverse extreme positions in correspondence with thetrack switch TS when it is locked, and assume intermediate positionsduring the operation of the switcher at such other times that it isunlocked. These movable contacts 18 and 19 make contact betweenrespective pairs of fixed contactswhen in nor- 1 mal extreme positionsand make contact between certain other respective pairs of fixedcontacts when in reverse extreme positions. A shunt contact 20 isactuated to a non-contacting position when the track switch TS? is in anormal locked position, and assumes a biased contacting position atanysuch-time that the track switch is not in a normal locked position; andalso, a shunt contact 21" is actuated to a non-contacting position whenthe track switch is in a reverse locked position, and assumes a biasedcontacting position at any such time that said track switch is not in areverse locked position.

Similarly the point detector contacts PD are associated with the trackswitch TS and include movable contacts 22 and 23, also shunt contacts 24and 25, which contacts have functions as above explained forcorresponding parts of the point detector contacts PD.

The point detector contacts PD and PD" may be operated by any suitabletype of mechanism, such for example as shown in the patent to C.SLBushnell, Patent No. 1,513,236, dated November 25, 1924 with theshuntcontacts added as shown, for example,

. in my pendingapplication Ser. No. 385,17 2,

filed August 12, 1929. i a 7 Local transformers LT and LT", located atthe switches TS and TS? respectively, are I supplied withsuitablealternating current potential from a transmission line 1extending from the interlocking tower.

In the interlocking tower, relays SS and SS are provided to indicate thepositions and phase windings 80and .31 resp'ectively'and local phasewindings 82 and33 respectively; The. l tel P a e wind 2% 133 are. n t;

switches.

tinuously energized from local transformers T and T respectively, whichtransformers are supplied with alternating current potential from thesame transmission line which supplies the local transformers at the 4The line phase windings 30 and 31 are respectively governed by the pointcletector contacts PD and PD".

The usual control levers L and L" arepro vided for controlling therespective switch machines SM and Slit-5". These levers are providedwith indication latch mechanisms IL and TL respectively which preventthe operation of the respective levers to full nor.- mal or full reversepositions from corresponding governing positions except after actuationof the associated indication magnets Il /l and 1M These indication latchmechanisms TL may be of any suitable type, such for example, as showninthe patent to J. D. Taylor, Patent No. 7 52,127,dated February 16,1904:. V sociated with their respective indication magnets 1M and 1M". 1The safety magnets S are designed tocarry the full operating current ofthe switch machine, and provide that the indication magnets 1M cannotactuate their armatures to release the indication lat-ch mechanisms ILwhile such operating current is flowing due to the ratio of turnsbetween the two windings and due to the fact that the safety magnetshave the advantage with the armatures against-their pole faces. Inaccordance with the present invention, the safety magnets S preventfurther falsereleasing of the indication lat-ch mechanisms shouldcrosses occur'between the operating wires or between the nextoperatingwire of a particular SWltCl'l machine and some foreign source,all of which will. he pointed out more specifically hereinafter. g

The levers L and L have associated therewith the usual tappet bars 35and 36frespec tively which are controlled by their respective cam slots37 and 38 for controlling the usual mechanical interlocking betweenassociated levers in a manner well known to those skilledin the art.usual reciprocating type operating their re spective movable contacts25, 26, (2'? and 28 to any one of four positions, namely, full normalpositions, half normal positions, half reverse positions and fullreversepositions in the order named as the levers. are moved to the leftfrom the normal positions shown; These movable contacts make contactbetween their respective pairslof fixedcontacts when in normal and half.normal positionsand make contact between certain other pairs of fixedcontacts'when in full reverse or half reverse T positions.

r In order that the respective levers L and L 'may 'be'provided withindications which will not Ptllllllilthfi. operation of a lever to aposition out of correspondence with its asso- Safety magnets S and S areas- The levers L are of the 1,0: the SS re-lays.

ciated switch machine, the indication selectors IS. and IS are provided,being of the usual' I I L and switch inachine'SMs will be describedmechanicalstick type. I I Polarized cross protection relays P and Pare'provided toop en the control circuits Of the respective associatedswitch machines should a cross-occur between the operating wlres'oi' aparticuljar SW1tCl1-1T12tCh1Il6 Qr between the next operating WHQ -O'f apart cular switch machine and some foreign sourc'e.'-lv

These polarized crossprotection relays may be of any suitable type, forexample, as shown July 10,

in my Patent No. 1,676,340 dated 1928. I

Suitable resistances R and R are provided inmultiple with the respectivefield windings F and F to reduce the alternating current impedance ofthe line circuits of the respective SS relays. Although the fieldwindings F are of low resistance to the direct current operating power,they are ofcomparatively high impedance to "the alternating current forthe SS relays. Thus, these resistances R and R reduce the impedancevaluesflof the SS relay line circuits as well as tending to provide abetter phase relationship as will be hereinafter pointed out.

of line wires which extend between the interlocking tower and the switchlocations. Also, these resistances provide means for 0htaining suitablerelative phase displacement between the local andline It is believedthatthe usefulness ofsucha system and the interrelated: functions of thevarious devices will bebetter understood by further description beinggiven irons the ;.standpoint ofopera-tion of the system taken as awhole.I I

Operation of the system The control levers L and L are shown in Y theirfull normal positions with their respective switch machines SM and SMincorre I sponding positions, Inaccordance therewith, the relays SSandSS are energized in 'a'manner to control their contacts to nor-.,

mal ositions, which contacts ,may be used in accordance with the usualinterlocking practice. It is to be understood that it is unnecessary toshow the means, and manner of" control accomplished by the contact oithe SS relays as such control iorins no'j iart i ofthe/presentinventionand'mejy be varied to suit the particular circumstances of givensituation.

Also, these resistances R are preferably of'a value equal-to thealternatmgcurrentimpedance of the respec- 7 phase windings of Only theoperation and interrelation of a the parts associated with the control.lever in detail, as the operation and interrelation of the parts anddevices associated with the control lever L and the switchmachine SM isidentical in every respect. However, the

tune-- interrelation between these-two switch tions will be set forth indetail. The local phase winding 32 of the relay SS iscontinuouslyenergized with alter-nating current supplied bythelocaltransformer former Ll located at the switch machine. The localtransformer LT 1s energmedirom the alternatmg current transmlssion lineex tending: trom t'he interlocking tower through point detector contactsPD which are in normal positions. lThlS normal energ1z1ng circuit'forthe local transformer LT is traced as follows :from one terminal of thealterand a3, primary winding of local transformer LT, wire 44, shuntcontact 21 in a contact ing position, contacts 19-45, wire 46,resistance 120, wire 47, to the opposite terminal of the alternatingcurrent source.

The energization ofthe primary winding of localtransformer LT causes thecurrent induced-infits secondary winding to 'flow in the normalenergizingcircuit of the line phase win dingof the relay SS. This normalI LDD energizing circuit is traced as--follows:

from the right hand terminal of thesecondsay of transformer LT, throughwires 48 and -49, field winding F and resistance R multiple, wire50,contacts 10 51, wire 52, armature A, wires 53 and 54, contacts ll55,wire 56 contacts- 57 wire 58, con- 1 tacts 5 9-60 of indication selectorIS, wire 61, line phase winding of relay, SS, wire 62, windings ofindication magnet 1M, wire 63, windings-of cross protection relay P wire64-,contacts 6566'67 of'relayP,wire 68,

to the left-hand terminal of thesec'ondary of: localjtransiormer Vi Y Y1 It is noted t-hat the usual practice isto supply the local phasewinding 'of-s'uchan SS relay with a'current having .a relatively largerreactive component than the line phase winding, as the local currentflows through I short lead wires tliusreducing the amount of pow-erloss, whiletlielinephasewindingis usually provided with a current havinga relatively larger resistive component as this current naturally has aresistive characters istic t due to the length of line wire 'andisof atethe relay contacts. However, in this case,

as considerablysmallervalue. This is o f course done to give asuitable'phase displacement the line phase winding circuit includes thefield winding F, the wlndlngs of indlcation magnet 1M and the windingsof polarized relay P all of which-tend to change the phase T angle ofthe line phase winding from a re.-

ample, allows one-hali of the line phase winding current to pass throughit thereby adding to its resistive component. Also, the

- resistance 120 as well eingcompensating means for the varying distancebetween the tower and the outlying switch machine, also adds to theresistive component of the line phase winding current.

Let us consider the operation of the system from the normal conditon'tothe reverse condition, which is accoi L ished by the operation of thecontrol lever L from its pres ent normal condition to a half reverseposition and thence to a full reverse position after thecompletedoperation'of the switch machine SM. The operation of the system om areverse condition to a normal condition willnot be described as it ismerely an inverse function thereof.

Assuming that the lever L is moved to a halt reverse position, thenormal energizing circuit of the line phase winding 30 of the relay SS"is broken at contacts2557 which immediately causes its contacts toassume neutral deenergized positions. Also, with the lever L in the halfreverse position, the i switch machine SM receives operating currentfrom a suitable source of direct current potential, the oppositeterminals oi which are shown as posltive and negative buses. V

The reverse operatlng clrcult of the switch ,machine SM is traced asfollows :from

lectorIS wire 78 contacts 2674 wires 75' 7 7 7 and 56, contacts 1155,wires 54 and 53, windings of armature A wire 52, contacts 1051, wire 50,field winding F and resist ance R in multiple, wires 49 and l8,secondary winding of local transformer LT, wire 68, contacts 676676 ofrelay P, wire 77, windings oat safety magnet S wire 78,

' to the negative bus of, the suitable source.

The operating current of the switch machine SM which flows through thiscircuit oper ates both the switch machine, and the contact 60 ofindication selector 1S to reverse positions.

Duringthe operation of thelswitcli ma} chine SM and as soon as it hasoperated to' unlock the track switch TS, the point detector contacts 18and 19 are operated to intermediate non-contacting positions whichallows the shunt contact 20 to ajssume'a contacting position. Theenergization of the primary of the local transformer LT isthusdiscontinued and. said primarywindingis short circuited or shuntedthrough wire 44, shunt contact '21 in a contacting position,

wire 79,shunt contactQO in-a contacting o;

bring the armature A to rest, and to prov vide energization oftheindication magnet 1M for releasing theindication latch mechanism ILwhich allows movement of the control lever L toa full reverse position.This reverse dynamic indication circuit for the switch machine SM istraced as follows :from the lower terminal of armature A through wire53, contacts 1082, wires 83 and 50, field win-ding F and resistance B inmultiple, wires 49 and 48, secondary winding of local transformer LTwire 68, contacts 67-v6665, wire. 64, windings of polarized relay P,wire 63, windings of indication magnet 1M, wire 62, line phase winding30 of relay SS, wire 61, contacts 608 l-' oi indication selector IS,wire 85, contacts 2586, wires 87, 88 and 89, contacts 11- 90, wires 91and 52, to the upper terminal of armature'A The dynamic current flowing'in'this circuit actuates the indication magnet IM but does not actuatethe contact 660i polarized cross-protection relay P, this because thisrelay P responds only to direct current of a' particular polarity,namely to current flowing from right to left through itswinding, itpreferably being a polar relay of the" permanent magnet ype;

Also, withthetrack switchlTS in'a reverse lOCkQClPOSltlOH the movablepoint detector contacts 18 and'll) are operated to reverse extremecontacting pOSltlOIlSnWhlCh cause the. shunt contact 21 to be operatedto. a non-contacting position. The primary winding of local transformerLT is thus energized through a circuit traced as fol lows :-'from oneterminal or" the alternating current source, through wires it) and 92,contacts: 1993, wire 4 4', primary winding of local transformer LT wire43 shunt contact 20 in a contactingposition, wire 94, contacts 18%95,wires 96 and 4:6, resistance 120,

rent induced when the point detector contacts PD are in normalpositions, and flows in the reverse energizing circuit for the linephase winding 30 of the relay S-S thus actuating its contacts from.deenergized positions to reverse energized positions. 1 This reverseenergizing current for line'phase winding-3 of relay SS is traced asfollows :fro-mz the right-hand terminal of the secondary of localtransformer LT, through'wir'es 48" and 49, ii'eld'winding F andresistance R in multiple, wires 50 and 83, contacts 82,wire 53, windingsof 'armatureA Wires (Band 91, contacts11 9'0, wires 89, 88 and 87,contacts 86, wire 85, contacts 84- 60 of indication selector IS wire 61,line phase winding of relay SS, wire 62, windings of indication magnetIM wire 6 3,winding' of polarized relay P2 wire 64, contacts 65-66-67,wire 68, to the left-hand terminal of the secondary of local transformerLT. I

During the operation of the switchmachine SM the movable contacts 14 and16 of the pole changer coil contacts PCC are operated to their centralintermediate contacting positions, which provides for the reversibilityofthe switch machine in midstroke by the operationof the control lever Lto an opposite governing' position. Such movement of the control leverapplies energy to the opposite control wire which completes a circuitfor the corresponding pole changer coil that operates the movablecontacts 10 and 11 of pole changer contacts PC to opposite positions toclosethe opposite operating circuit. This is accomplished all in amanner as disclosed in the above mentioned Patent No. 1,466,903.

From the above description, it is obvious that-the dynamic indicationcircuits. and the energizing circuitsfor the line phase winding 30' ofthe relay SStfare very similar the vvarious devices and contacts whichthey'inelude. However, they'differ 1n the character of currents, thesources of such currents: and the devices which are actedupon by suchcurrents. More; specifically, the dynamic indication current is directcurrent generated by the revolving armature ofthe direct current motorincluded within the switch machine, while the energizingcurrent for theSS relay is alternating current supplied to the circuit by a localtransformerhaving its secondary winding included therein. Thedynamic-indication current actu ates the indication magnet IM, but doesnot actuate the polarized relay P, as this relay requires theapplicationof positive potential upon its right-hand terminal in, orderfor its contacts to be, actu'-' ated; and does not actuate the rel-ayeas it is of the twophase alternating current type an'd obviously cannotoperate withthe application of direct current. The alternatingindication current] for the SS relay flows through thesame circuits butisof such a comparatively small valuethat it doesnot effeet theindication magnet 11%, or polarized cross protection relay Pflbut doesactuate the line phase winding 30 of-the SS relay.

' Although the resistance R is in multiple with the field winding Fthere is a very small "value of the operating current which flowsthrough R asit is of such high ohmic resistance in comparision-withi theohmicresistance of the Field windingl However, with the applicationofalternating current across themultiple circuit of the field. windingand resistance, thealernating current impedance of the field winding inaccordance with -the frequency of thecurrent is equal tothe ohmicresistance of .the resistance R. The alternating current thus dividesequally between the two.

Assumingthe switch machineSM and control leverL- to hem normal"positions,- asshown, and that a cross 0 occursbetwcen the twocontrolwires 56' and 8810f the switch-inachine SM an unauthorized current wouldlay P wire 64, contacts 66',76 wire 77,

windings of safety magnet S, wire 78', to the negative bus. Currentflowingthrough this circuitestablished by an accidental cross betweenthe control wires of switch machine "SM operates the contact 66 of crossprotection relay P to an upper position opening contacts 66-7 6, whichopens both the normal and reverse operating-circuits of the switchmachine SM and also o'pens'the cross Cir-- cuit. Duringthe existence ofsuch a cross,'as for example C the current that flows in said circuitpasses through the safety magnet S and indication magnet IM in series,thus preventing said current from actuating or falsely releasing theindication latch mechanism IL? for reasonsabov'e pointed'out.

Should'the cross protection circuit for the.v switch machine SM as'abovep'ointed out, for any reason be incomplete, it is obvious that therelay SS would be} deenergized, as its normal and reverse energizingcircuits include respectively'the normal and reverse cross protectioncircuits of the switch, ma chine. Thus, itv may be said that the relaySS provides a check upon the cross protection of the switch machine SM.c

. Shouldcross C occur betweenthe norwas mal control wire 102 of theswitch machine SM and the reverse control wire 56 of switch machine SMthe switch machine SM" would not 'be operated due to the fact that thecross protection relay P would be operated to open the control circuit.However, heretofore there has been the possibility that such a cross,between the control wires of two such similarly Controlled functions,would energize the indication magnet 1M and falsely actuate theindication latch mechanism IL. This is prevented by thepresent inventioninasmuch as the safety magnet S is-included in series with indicationmagnet IMf if such a cross circuit occurs, which prevents the actuationof the armature of indication magnet IM to an energized position 'forreasons heretofore pointed out. This unauthorized circuit, establishedby a cross such as cross 0 may be traced as follows :'from the positivebus, through wiresll and 115, normal operating coil 116 of indicationselectorIS wire 117, contacts 281l8, wire 102, cross circuit C wire 56,contacts 25-57, wire 58, contacts 59-60 of indication selector IS,

' wire 61, line phase winding 30 of relay SS,

wire 62, windings of indication magnet 1M, wire 63, windings ofpolarized crossprotection relay P wire 64:, contacts 656676, wire'77,windings of safety magnet S wire 78, to the negative bus. Thecontact 66of polarized cross protectionrelay P is actuated to an upper positionopening the operating circuit of the switch machine SM at contacts666776, and opening the unauthorized circuit at contacts 656676.

The safety magnet S is located in a key position which provides that itmay always carry the operating current of its associated switch machineSM; and that it may be included in series with its associated indicationmagnet Ill/l when any false or unauthorized circuit occurs which mightfalsely ener ize said indication magnet.

The safety magnets S have the further functions of preventing theenergization of their associated SS relays from any other alternatingcurrent sources used to energize other similarly connected SS relays.This may be explained by considering, for'eX- ample, cross C which mightoccur:between the reverse operating wire 103 of switch ma chine SM andthe reverse operating wire 56 of switch machine S1 lVith such a crosscircuit, theline phase winding 30 of relay SS would be falsely energizedor falsely afiected by the local transformer LT during the time that anysuch cross should occur,if it were not for the added impedance in thecircuit provided by the safety magnets S. This unauthorized circuit maybe traced as follows :-from the righthand terminal of the secondary oftransformer LT, through wires 105 and 106, field winding F andresistance R connected in multiple, wire 107, contacts wire 64:,contacts 656676, wire lngs of safety magnet S, wire 78, through wire 58,contacts 59-60 of indication selector IS, wire 61, line phase winding 30of relay SS wire 62, windings of indication magnet IM wire 63, windingof polarized relay P,

77, windthe negative bus, wire 113, windings of safety magnet S wire121, contacts 122123-124 of polarized relay P wire 125, to the leftiandterminal of the secondary of local transformer LT". The'current, whichwould flow through this circuit, should such cross occur, is ofinsuilicient value to operate relay SS This is determined by theprovision of the safety magnets S and S positioned in the common ornegativereturn wires of the respective switch machine function, as theircombined impedance adds to the regular impedance in the line phasewinding circuit of the relay SS, an. amount sufiicient to limit thecurrent which may flow therein to a value beneath the operating value ofsuch an SS relay. I

If a cross should occur between wire 56 and wire 68, the line phasewinding 30 of the SS relay would be shunted in a manner to cause itsdeenergization. Also,' '1t would be necessary'for a break to occur inwire 56 and a break in wire 68 with these broken wires connectedtogether in a reverse manner in order for a false active indication tobe displayed by the relay SS As. is well lmown to those skilled in theart, such an occurrence is very remotely possible. If such a case didoccur, it would be immediately detected upon the next operation of thecontrol lever.

' Thus, the present invention provides an interlocking system, which iseffectively protected from crosses that may occur within the controlcircuits of a particular function, and which is effectively protectedfrom crosses from-other vremotely controlled functions.

The present invention further provides a superimposed alternatingcurrent indication system for giving a reliable indication of theposition and locked condition of its associated switch machine, whichsystem checks the cross protectioncircuits of the switch machine, aswell as, in itself being protected from crosses with other similarindication systems.

' Although the operation of the switch machine function SM hasbeen morespecifically pointed out, and although the relationship of this functionhas beenvmore specifically :pointed out with reference to the switch ma-1 chine function SM, it is to be understood that Ill) sible innumerablecombinations of unauthori ized conditions, which it: is obviously impossible to specifically. point out. However, those specific abnormalconditions which havebeen' pointed out are to be considered as merelyillustrative of those other conditions which might occur; In otherwords, it is intended that a particular switch machine function is tobeprotected from improper operation or indication the, application ofunauthorized positive potential, that is, a potential, which is positiveinrespect to the. negative bus, to its next operating wire regardless ofits present position, whether such potential may be applied fromanotherzsimilari function in a similar position or in a differentposition or from any foreign source. Protection of an SS relay fromoperationfrom the energizing source of any other similarly operated SSrelay is to be provided. regardless of the positions of the function'sinvolved in the unauthorized cross circuits. I

Having described: an indication system of one type as supenimposed uponan interlocking system forpurposes heretofore set forth,

as one specific embodiment of the present invention, itisdesired to beunderstood that this fOllll'lS selected to facilitate in thedisclosure-of: the invention rather than to limit the'number of formswhich'it may assume; and, it to be further understood that variousmodifications,adaptations. and alterations may be applied: to thespecific form shown to meet the requirements of practice,

without in any manner departing. from the spi'ritorfscope of thepresentinvention except as: limited: by the appended. claims.

, Having described my invention, I new claim i 1. In aninterlockingsystem for railroads, a track switch, a switch machine, acontrol lever, two operating wires and a common return wireinter-connecting said switch'machine and said control lever, contactsoperated by said lever to establish normal and reverse control circuits,also normal and reverse dynamic indication circuits, a source ofelectrical potential having positive and negative terminals, anindication selector having normal and reverse operating coils includedin said normal and reverse control circuits respectively and havingcontacts included in said normal and reverse dynamic indicationcircuits, an indication magnet included in said normal and reverseindication circuits, a cross protection relay included in said normaland reverse indication circuits, and a safety magnet included in thecommon connection of said control circuits to the negative terminal ofsaid source and not'included in said common wire.

.2. In an interlocking system for-railroads, a track switch, a switchmachine, a controllever,two operating wires and a common return namicindication circuits, a source of direct current electrical potentialhaving positive and negative terminals, an. indication selector havingnormal and reverse operating coils included in said normal and reversecontrol circuits respectively, and having contractsincluded in saidnormal and reverse dynamic indication c rcuits, an indication magnetincluded in's'aid normal and reverse indication circuits, a crossprotection relay included in said normal and reverse indicationc1rcu1ts,:a safety magnet included in the commonconnection ofsaidcontrol circuits to the negative terminal of said source and notincluded. in said common wire, an 'electro-responsive device includedill-Said dynamic indication circuit which device is not responsive todynamic indication current, and means applying energizing current tosaid dynamic indication circuit to which said electroresponsive devicewill respond and thereby indicate the condition of saidtrackswitch. V v

I 3. In an interlocking system, a track s-w1tch,a"s-w1tch mach1ne,-acontrol lever, a

source of electrical energy, means for completi'ng normal and reverse?control circuits from said source tossaid switch machine, means forcompleting normal and reverse dynamic indication circuits, dynamicindication responsive means for governing the movement of said controllever'included in said normal and reverse dynamic indication circuits,an. electroresponsive device included in said dynamic indication circuitbut unresponsive to dynamicindication current, alternating currentenergizing means for actuating said electroresponsive deviceinaccordancewith the condition of said track switch but ineffective foractuating said dynamic indication, responsive means, and safety meansfor preventing'the operation of said dynamic indication responsivedevice during the flow of current in said control circuits, and duringthe flow of current in said indication circuits when said flowisopposite to the normal direction of flow of said dynamic indicationcurrent, and for preventing the flow of alternating current from saidenergizing means to said source of electrical energy.

4.. Inccombination with electric interlock systems comprising, anelectro-responsive device responsive to alternating current only, saiddev ce having a local phase wind- =in-g and a line phase winding, meansfor energlz ng said local phase winding,- means for energizing said linephase winding in ac- Zlil 0 cordance withthe condition of a particularinterlocking system, means for relatively adjusting the phasedisplacement between. the currents in said local andsaid line phasewindings, and cross protection means protecting each one ofsaidindication systems from every other one of said indication systems.

5. In an interlocking system for railroads, a track switch, a switchmachine having an armature and a field winding, a control lever, twooperating wires and a common return wire, a source of direct currentelectrical potential having positive and negative terminals, contactsoperated by said control lever for establishing normal and reverseoperating circuits, also normal and reverse dynamic indication circuitsfor said switch machine over said operating wires and said common returnWire, an indication selector having normal and reverse operating coilsincluded respectively in said normal and reverse operating circuits andhaving contacts included in said normal and reverse dynamic indicationcircuits, an indication magnet included in said dynamic indicationcircuits, a safety magnet included in the common connection of saidoperating circuits to said negative terminal of said source of directcurrent potential, a polarized relay included in said dynamic indicationcircuits and unresponsive to the dynamic indication current flow ingtherein but responsive to current vof an opposite polarity, said relayhaving contacts for opening said common connection of said operatingcircuits to said negative terminal of said source, an alternatingcurrent electroresponsive device included in said dynamic indicationcircuits only and being unresponsive to direct current, means forsuperimposing alternating current upon said dynamic indication circuitsin accordance with the position of said track switch, means forrelatively adjusting the ratio between the reactive and resistivecurrent components of said alternating current used to actuate saidalternating current 'electro-responsive device, said means including aresistance in multiple with said field winding and another resistance inseries with said means for superimposing alternating current upon saiddynamic indication circuits. 7

6. In an interlocking system; the combination with a switch machine; alever; a nor- 1211 and a reverse control wire and a common wire leadingfrom said lever to said switch -machine; a dynamic indication magnet; a

safety magnet acting in opposition to said indication magnet; .a sourceof current; a normal circuit for said switch machine including saidnormal wire, said common wire, said safety magnet and said source inseries,

and with said safety magnet in the lead wire from one terminal of saidsource; a reverse circuit for said switch machlne lncludlng said reversewire, safety magnet and sald source in series,

safety magnet acting lndlcittlOll magnet; a source of current; a

said common wire, said and with said safety magnet in said lead wire;and an indication circuit including said reverse wire, the motor of saidswitch machine, said common wire and said-in:- dication magnet inseries, and with said lead wire connected to'the junction of said commonwire with said indication magnet, whereby it imauthoiized current flowsthrough said indication magnet and to said source it also flows throughsaid safety magnet and prevents operation of said indication magnet. V 1l 7. In an interlocking system ;the combination with a switch machine; alever; a normal anda reverse control wire and a common wire leading fromsaid lever to said switch machine; a dynamic in opposition to saidnormal circuit for said switch machine including said normal wire, saidcommon wire, said safety magnet and said'sourcein series, and with saidsafety magnet in the lead wire from oneterminal. otsaid source and saidcommon wire connected to said lead wire; a reverse circuit for saidswitch machine including said reverse wire, said common wire, saidsafety magnet and said source in-serie's, and with said safety: magnetin said lead wire; and an indication circut including said reverse wire,the motor'of said switch machine, said common wire and saidindicationmagnet, whereby if unauthorized current flows through said indicationmagnet and to said source it also flows through said safety magnet andprevents operation of said in dication magnet.

In testimony whereof I atfix my signature.

JOHN G. LI'NDNER.

indication magnet; a"

